The invention relates generally to depth profiling and more particularly to depth profiling using laser plasma spectroscopy.
Exposure to high temperatures for extended periods of time can damage metal parts of machinery such as buckets, blades, and nozzles in turbine engines. In gas turbine engines, such damage can result in a reduction in airflow and thus efficiency. Damage to blades can eventually lead to failure of the engine. Coatings are frequently used to protect metal parts such as turbine blades from the effects of high temperature exposure for extended time periods that can damage the blades and reduce lifetime. Although the coatings extend the lifetime of the metal components, the coatings themselves are affected by this exposure over time.
Currently, all the buckets, blades, and nozzles are stripped and recoated after a given exposure interval, or the engine is partially disassembled and a sample part is removed and sacrificed for analysis. Both procedures result in lengthy outage times. However, it has been recognized that lifetime of the coatings can be predicted by the concentration of various elements in the coating as a function of depth. Although a number of analytical techniques exist for measuring elemental concentration as a function of depth, they all either invoke destructive analysis of the part or substrate (e.g., secondary ion mass spectroscopy and electron microprobe analysis) or cannot be performed remotely or in situ (e.g., laser ablation mass spectroscopy), especially in real time.
Therefore there is a need for an in situ and near real-time analysis technique for depth profiling, which is nondestructive to the substrate and which removes the need for disassembling the machinery.